1. Field of the Invention
This invention relates to a control system for hybrid vehicles having an internal combustion engine and a traction motor as prime movers.
2. Prior Art
Conventionally, a hybrid vehicle having an internal combustion engine (hereinafter simply referred to as "the engine") and a traction motor as prime movers is widely known, and a control system for controlling the prime movers of such a hybrid vehicle has already been proposed e.g. by Japanese Patent Laid-Open Patent Publication (Kokai) No. 5-229351.
The proposed control system determines the optimum torque at which the maximum engine efficiency is attained, in dependence on traveling conditions of the vehicle, and at the same time detects actual torque generated by the engine for actually driving the vehicle. Then, the control system determines or selects demanded or required torque from the optimum torque and the actual torque. When the optimum torque is selected as the demanded torque, and at the same time, the optimum torque is larger than the actual torque, regenerative current is caused to be generated for regeneration of energy (specifically, electrical energy).
In the above publication, it is not clearly shown that the regeneration of electrical energy is carried out during deceleration of the vehicle. However, it is presumed that when conditions for generating the regenerative current are fulfilled during deceleration of the vehicle, the regeneration of electrical energy is permitted. However, during deceleration of the vehicle, normally, the engine has its throttle valve fully closed, and hence there occurs a pumping loss, which prevents the vehicle's kinetic energy from being efficiently utilized for regeneration of electrical energy.